TW201429301A - Dimming circuit and lighting device using the same - Google Patents

Abstract

A dimming circuit and a lighting device using the same are provided. The dimming circuit comprises an interface trigger unit, an average duty cycle calculating unit, a control voltage calculating unit and a comparing unit. The interface trigger unit receives an on-time from each period in a PWM signal. The average duty cycle calculating unit is coupled to the interface trigger unit and calculates a ratio of the on-time to the period. The control voltage calculating unit is coupled to the average duty cycle calculating unit, and calculates a desired voltage according to the ratio. The comparing unit is coupled to the control voltage calculating unit, and sends the desired voltage and a differential voltage to a driving circuit.

Description

Dimming circuit and light emitting device using same

The invention relates to a dimming circuit and a lighting device using the same, in particular to a dimming circuit for adjusting a light emitting diode and a lighting device using the same.

The conventional dimming method is a series connection of a variable resistor in the circuit for controlling the load current flowing through the circuit, but the resistor consumes energy in the circuit, so that the luminous efficiency is not good.

Pulse Width Modulation (PWM) can be used to adjust the light of lighting equipment due to its low noise and low energy consumption. Pulse width modulation is dimmed by discontinuous current. When the output is not 100%, some current will be zero before each output period of pulse width modulation, showing a dark state. The desired dimming effect is achieved by adjusting the ratio of the dark state to the bright state. Generally, the signal width of the pulse width modulation is greater than 1 kHz, which is higher than the visible range of the human eye, so the user does not feel the flicker.

However, if photography is required, if the scanning frequency of the photographic equipment is less than the operating frequency of the pulse width modulation signal for dimming, a flicker will occur, and the image will appear plaid, which will distort the image quality.

In addition, when the pulse width modulation is set to be low, the light source may flicker due to insufficient current.

The invention relates to a dimming circuit and a lighting device using the same, which can improve the problem of flickering and flickering during low conduction.

According to an embodiment of the present invention, a dimming circuit is provided, including an interface triggering unit, an average duty cycle calculating unit, a control voltage calculating unit, and a comparing unit. The interface trigger unit receives the on-time of the pulse width of each period of the pulse width modulation signal. The average duty cycle calculation unit is coupled to the interface trigger unit, and calculates a ratio of the on-time of the output of the interface trigger unit to the period. The control voltage calculation unit is coupled to the average duty cycle calculation unit, and calculates the required voltage according to the ratio calculated by the average duty cycle calculation unit. The comparison unit is coupled to the control voltage calculation unit, and calculates a difference voltage with the feedback voltage according to the required voltage calculated by the control voltage calculation unit, and transmits the required voltage and the difference voltage to the drive circuit.

According to an embodiment of the present invention, a light emitting device including a light emitting diode, a driving circuit, and a dimming circuit is provided. The driving circuit controls the light emitting diode to emit light. The dimming circuit includes an interface triggering unit, an average duty cycle calculating unit, a control voltage calculating unit, and a comparing unit. The interface triggering unit receives the on-time of the pulse width of each period of the first pulse width modulation signal. The average duty cycle calculation unit is coupled to the interface trigger unit, and calculates a ratio of the on-time of the output of the interface trigger unit to the period. The control voltage calculation unit is coupled to the average duty cycle calculation unit, and calculates the required voltage according to the ratio calculated by the average duty cycle calculation unit. The comparison unit is coupled to the control voltage calculation unit, and calculates a difference voltage with the feedback voltage according to the required voltage calculated by the control voltage calculation unit, and transmits the required voltage and the difference voltage to the drive circuit. The driving circuit compensates the control voltage output to the LED according to the difference voltage. Control voltage is based on the second pulse The width of the second pulse width modulation signal is greater than the frequency of the first pulse width modulation signal.

In order to provide a better understanding of the above and other aspects of the present invention, the following detailed description of the embodiments and the accompanying drawings

FIG. 1 is a functional block diagram of a dimming circuit according to an embodiment of the invention. The dimming circuit 100 includes an interface triggering unit 110, an average duty cycle calculating unit 120, a control voltage calculating unit 130, and a comparing unit 140.

The interface triggering unit 110 is configured to receive an external first pulse width modulation (PWM) signal S, and convert the positive edge and the negative edge of the pulse width into a trigger signal for performing an operation. For example, please refer to FIG. 2A, which illustrates a voltage versus time relationship of a pulse width modulation signal having a forward waveform. The rise of the voltage value is called the positive edge, and the drop of the voltage value is called the negative edge. A pulse wave has a positive edge and a negative edge. The PWM signal shown in FIG. 2A includes two positive edges P _n , P _n+1 and two negative edges N _n , N _n+1 , which will be converted into a picture as shown in FIG. 2B after the interface is triggered by the interface. The trigger signal r records the position of the positive and negative edges.

In this embodiment, since the pulse width modulation signal of the forward waveform is provided (FIG. 2A), the time interval between the two adjacent positive edges P _n and P _n+1 is the pulse width modulation signal. The period T _PWM , and the time interval from the positive edge P _n to the next negative edge N _n is the on-time T _ON of the pulse width of this period. When the pulse width modulation signal is provided as a reverse waveform (not shown), the interval time from the negative edge to the next positive edge is the on time, and the interval time from the negative edge to the next positive edge is the on time.

The average duty cycle calculation unit 120 is coupled to the interface trigger unit for calculating a duty cycle of the first pulse width modulation signal S, that is, a ratio of the on time to the cycle. The calculation formula for the work cycle is:

Where D represents the duty cycle, T _ON represents the on-time, and T _PWM represents the cycle. For example, if the period of a pulse width modulation signal is 1 second and the on time is 0.2 seconds, the duty cycle is 20%. If the period and the on-time of the pulse width modulation signal are constant values, the duty cycle of each pulse wave is equal to the duty cycle of the entire pulse width modulation signal. If the period and the on-time of each pulse wave of the pulse width modulation signal change, the average duty cycle calculation unit 120 calculates the duty cycle of each pulse wave, and obtains an average value of the duty cycles.

The control voltage calculation unit 130 is coupled to the average duty cycle calculation unit 120 to calculate the required voltage V ₁ when the output current is DC according to the average duty cycle output by the average duty cycle calculation unit 120. For example, if the voltage of the first pulse width modulation signal S is 5 volts and the average duty cycle is 20%, the required voltage is 5×20%=1 volts.

The comparison unit 140 is coupled to the control voltage calculation unit 130 for transmitting the required voltage V ₁ to the driving circuit of the light source, for example, the driving circuit 300 of FIG. 1 for dimming.

In an embodiment, the dimming circuit 100 further includes a feedback unit 150 for compensating for energy lost in the circuit. The feedback unit 150 is coupled between the comparison unit 140 and the driving circuit 300 of the light source for converting the output current outputted by the driving circuit to the light source into the feedback voltage V ₂ , and outputting the feedback voltage V ₂ to the comparison unit. 140. In this embodiment, after receiving the feedback voltage V ₂ , the comparison unit 140 calculates the difference voltage V _D between the feedback voltage V ₂ and the required voltage V ₁ , and simultaneously transmits the required voltage V ₁ and the difference voltage V _D to Drive circuit 300.

In summary, the dimming circuit 100 can accept a pulse width modulation dimming signal of a different frequency from Hz-kHz and convert it into a specific required voltage V ₁ , thereby changing the continuous current whose output current is DC. Maintaining the low loss of the pulse width modulation signal can also improve the flashing of the source when the flash frequency and low conduction.

In an embodiment, the dimming circuit 100 can be used in the field of illumination. For example, referring to FIG. 1, a light-emitting device 10 includes the above-described dimming circuit 100, a light-emitting diode 200, and a driving circuit 300. The driving circuit 300 is coupled to the dimming circuit 100 and the LED diode 200 to receive the dimming signal (difference voltage V _D , the required voltage V ₁ ) emitted by the dimming circuit 100 to generate a control voltage V _{C to} drive the LED Body 200.

In this example, the driving circuit 300 further includes a rectifier 310, a power stage 320, and a low-pass filter 330.

The rectifier 310 is coupled to the external voltage U. When the external voltage U is alternating current, the rectifier can convert it to direct current.

The power stage 320 is coupled between the rectifier 310 and the comparison unit 140 of the dimming circuit 100 for converting the external voltage U into the control voltage V _C according to the required voltage V ₁ and the difference voltage V _D output by the comparison unit 140. . In one embodiment, the control voltage V _C can be generated according to the second pulse width modulation signal (not shown) of the driving circuit 300. Preferably, the second pulse width modulation signal is a high frequency signal having a frequency greater than a frequency of the first pulse width modulation signal. That is to say, regardless of the first pulse width modulation signal frequency of the external input, the pulse width modulation signal output to the power stage 320 is a high frequency. In one example, the frequency of the second pulse width modulation number is greater than 20 kHz, and the frequency of the first pulse width modulation signal is less than 5 kHz.

The low pass filter 330 is capable of allowing low frequency signals to pass, but attenuating signals having a frequency higher than the cutoff frequency to pass the waveform of the control voltage to direct current.

In conclusion, the present invention has been disclosed in the above embodiments, but it is not intended to limit the present invention. A person skilled in the art can make various changes and modifications without departing from the spirit and scope of the invention. Therefore, the scope of the invention is defined by the scope of the appended claims.

10‧‧‧Lighting device

100‧‧‧ dimming circuit

110‧‧‧Interface trigger unit

120‧‧‧Average duty cycle calculation unit

130‧‧‧Control voltage calculation unit

140‧‧‧Comparative unit

150‧‧‧return unit

200‧‧‧Lighting diode

300‧‧‧ drive circuit

310‧‧‧Rectifier

320‧‧‧Power level

330‧‧‧low pass filter

N _n , N _n+1 ‧‧‧ negative margin

P _n , P _n+1 ‧‧‧

R‧‧‧ trigger signal

S‧‧‧First pulse width modulation signal

T _ON ‧‧‧ On time

T _PWM ‧‧ ‧cycle

U‧‧‧ external voltage

V ₁ ‧‧‧required voltage

V ₂ ‧‧‧Responsive voltage

V _C ‧‧‧Control voltage

V _D ‧‧ ‧ difference voltage

FIG. 1 is a functional block diagram of a dimming circuit according to an embodiment of the invention.

FIG. 2A is a diagram showing voltage versus time of a pulse width modulation signal having a forward waveform.

FIG. 2B is a schematic diagram showing the pulse width modulation signal of FIG. 2A after passing through the interface trigger unit of the present invention.

10‧‧‧Lighting device

100‧‧‧ dimming circuit

110‧‧‧Interface trigger unit

120‧‧‧Average duty cycle calculation unit

130‧‧‧Control voltage calculation unit

140‧‧‧Comparative unit

150‧‧‧return unit

200‧‧‧Lighting diode

300‧‧‧ drive circuit

310‧‧‧Rectifier

320‧‧‧Power level

330‧‧‧low pass filter

S‧‧‧First pulse width modulation signal

U‧‧‧ external voltage

V ₁ ‧‧‧required voltage

V ₂ ‧‧‧Responsive voltage

V _C ‧‧‧Control voltage

V _D ‧‧ ‧ difference voltage

Claims (10)

A light-emitting diode dimming circuit includes: an interface triggering unit that receives an on-time of each pulse width of a plurality of cycles of a pulse width modulation (PWM) signal; and an average duty cycle calculation The unit is coupled to the interface trigger unit for calculating a ratio of the on-times output by the interface trigger unit to the periods; a control voltage calculation unit coupled to the average duty cycle calculation unit, and based on the average The ratio calculated by the duty cycle calculation unit calculates a required voltage; and a comparison unit coupled to the control voltage calculation unit and calculates the required voltage according to the control voltage calculation unit, and calculates the required voltage A difference voltage of the voltage is fed back, and the required voltage and the difference voltage are transmitted to a light emitting diode driving circuit. The illuminating diode dimming circuit of claim 1, further comprising: a feedback unit coupled between the illuminating diode driving circuit and the comparing unit for illuminating the illuminating diode An output current output from the body driving circuit to a light emitting diode is converted into the feedback voltage, and the feedback voltage is output to the comparing unit. The illuminating diode dimming circuit of claim 1, wherein the interface triggering unit converts a positive edge and a negative edge of each pulse width of the pulse width modulation signal into a plurality of trigger signals, and The trigger signals calculate the on-times. A light-emitting device without a flash frequency, comprising: a light-emitting diode; a driving circuit for controlling the light-emitting diode; and a light-modulating circuit comprising: an interface triggering unit for obtaining a first pulse width modulation An on-time of each pulse width of the plurality of periods of the signal; an average duty cycle calculation unit coupled to the interface trigger unit, and calculating a ratio of the on-times output by the interface trigger unit to the periods; a control voltage calculation unit coupled to the average duty cycle calculation unit, and calculating a required voltage according to the ratio output by the average duty cycle calculation unit; and a comparison unit coupled to the control voltage output unit, and according to Calculating the required voltage calculated by the control voltage calculation unit, calculating a difference voltage between the required voltage and one of the feedback voltages of the LED, and transmitting the required voltage and the difference voltage to the driving a circuit, wherein the driving circuit compensates a control voltage outputted to the LED according to the difference voltage, wherein the control voltage is based on a second pulse width modulation signal Generating a second frequency of the PWM signal is greater than a first frequency of the PWM signals. The illuminating device of the fourth embodiment of the invention, wherein the dimming circuit further comprises: a feedback unit coupled between the driving circuit and the comparing unit for outputting the driving circuit An output current of the light emitting diode is converted into the feedback voltage, and the feedback voltage is output to the comparison unit. The device of claim 4, wherein the interface triggering unit converts a positive edge and a negative edge of each pulse width of the first pulse width modulation signal into a plurality of trigger signals, and The on-times are calculated from the trigger signals. The strobe-free illuminating device of claim 4, wherein the frequency of the second pulse width modulation signal of the driving circuit is greater than 20 kHz, and the frequency of the first pulse width modulation signal is less than 5 kHz. The flash-free lighting device of claim 4, wherein the driving circuit comprises a rectifier for converting the external voltage from alternating current to direct current. The flash-free lighting device of claim 8, wherein the driving circuit further comprises a power stage, wherein the power level is based on the required voltage and the difference voltage output by the comparing unit. An external voltage is converted to the control voltage of the light emitting diode. The flash-free illumination device of claim 8, wherein the driving circuit further comprises a low-pass filter to bring the waveform of the control voltage to direct current.